The present invention relates to an apparatus for receiving an optical signal transmitted from a remote control and converting the signal to an electric signal. More particularly, the present invention relates to a signal receiver for a remote control system in which a photodetector is disposed so as to have a directivity thereof substantially perpendicular to a direction in which a light enters through a front panel window.
There have been conventionally provided a variety of signal receivers which comprise a light guide for guiding an optical signal passing through a window toward a photodetector mounted on a circuit board. For example, a signal receiver is known which is designed to improve the strength of the light guide and permit a light to be received at various angles by making, out of a translucent resin material, the columnar portion of the light guide integrally with ribs for strengthening it (e.g., Japanese Utility Model No. 3041970).
There is also known a signal receiver which is configured to provide a front panel of the receiver with a tunnel through which an optical signal passes so that the optical signal is reflected by the inner wall of the tunnel to be guided to a photodetector (e.g., Japanese Patent Laid-open Publication No. HEI 10-210578).
A signal receiver is also known which employs an optical fiber as a light guide for guiding an optical signal (e.g., Japanese Utility Model Laid-open Publication No. SHO 63-181085). In a tape deck, there is known a light guiding apparatus capable of detecting the starting and ending points of a tape by guiding a light with an optical fiber in the same manner as the above (e.g., Japanese Patent Laid-open Publication No. HEI 7-220326).
Further, there is known a signal receiver which has a plurality of reflection surfaces on the surface of a light guide to permit a reflection of a light entering a window in arbitrary directions, thereby causing the relative position between the window and a photodetector to be set freely (e.g., Japanese Patent Laid-open Publication No. HEI 5-199179).
FIGS. 5 and 6 show a known signal receiver which is configured to guide an optical signal entering through a window of a front panel 2 toward a photodetector 4 through a light guide 9 of a substantially rectangular column (e.g., Japanese Utility Model No. 3065309). Here, FIG. 6 illustrates a C-C section of the light guide 9 and the same section of a metal mold 10 for forming the light guide 9. It can be seen that, when the metal mold 10 is configured rectangular in section, a shrinkage by cooling after molding causes the light guide 9 to have a section where each side is hollow in the middle with respect to the metal mold 10.
Further, a signal receiver is known that has a front panel provided with a stand for holding a circuit board (e.g., Japanese Utility Model Laid-open Publication Nos. SHO 59-44085 and SHO 64-33793).
As shown in FIG. 5, in a signal receiver for a remote control system or the like, a circuit board 3 is typically disposed adjacent to the bottom of the receiver at substantially a right angle to the front panel 2 so as to make the receiver small. The photodetector 4 is generally mounted directly on the circuit board 3 without a frame or other mounting construction, as disclosed in Japanese Utility Model No. 3065309, so as to enhance the freedom in design and reduce in production cost of the receiver. The photodetector 4 mounted directly on the circuit board 3 has a directivity in the normal direction on the circuit board 3, that is, at substantially a right angle to a direction of incidence L1 of an optical signal passing through the window of the front panel 2. Thus, it is required to guide the optical signal by using the light guide 9 so as to change its direction at substantially a right angle.
In the signal receiver disclosed in Japanese Utility Model No. 3041970, however, it is not taken into consideration to enable the light guide to change the direction of an optical signal at substantially a right angle, thereby the receiver failing to mount the photodetector directly on the circuit board. The signal receiver disclosed in Japanese Patent Laid-open Publication No. HEI 10-210578 is configured to guide an optical signal toward the photodetector mounted directly on the circuit board by bending the tunnel. However, the window in the receiver is configured to be open, thereby failing to prevent an invasion of foreign substances. If a foreign substance enters onto the photodetector, the photodetection performance of the receiver is markedly reduced. Thus, it is required some step such as covering the window with a transparent member. Such a step, however, causes the range within which a light can be received to be extremely limited due to the influence of surface reflection, thus a problem may arise in utility.
The receiver disclosed in Japanese Utility Model Laid-open Publication No. SHO 63-181085 and the apparatus disclosed in Japanese Patent Laid-open Publication No. HEI 7-220326 employ an optical fiber as a light guide to be remarkably limited in angle at which a light can be received. Thus, such a configuration is not suitable for a signal receiver which requires receiving optical signals emitted from various directions. Additionally, an optical fiber is expensive due to its two-layered structure consisting essentially of a core layer and a clad layer, thereby increasing the production cost of the receiver.
In the signal receiver disclosed in Japanese Patent Laid-open Publication No. HEI 5-199179, it is necessary to deposit a reflection layer made of aluminum or the like onto the outside of the reflection surfaces of the light guide. Thus, the receiver is increased in production cost. Further, the light guide disclosed in the above has a substantially rectangular cross section and has angular portions at the outside. In such a configuration, a light may leak through the angular portion, then the efficiency in utilizing a light is lowered. The signal receiver disclosed in Japanese Utility Model No. 3065309 has the same problem as the above.
Additionally, in the receiver disclosed in Japanese Utility Model No. 3065309, the photodetector 4 has a light-receptive potion 41 of substantially dome shape while the light guide 9 has a substantially rectangular cross section. Such a configuration prevents the light-receptive portion 41 from receiving a light reflected from the vicinity of the corner in the cross section, thus lowering the light utilization. As the light guide 9 is made of a synthetic resin, it is easy to reduce the production cost of the receiver. However, when the metal mold 10 for use in molding of the light guide 9 is configured to have a rectangular section as shown in FIG. 6, the shrinkage caused by cooling further lowers the light utilization. Accordingly, it is required to take the shrinkage into consideration in designing a metal mold for the light guide 9 having a substantially rectangular cross section, so the designing needs skills. Further, in the signal receiver, an exit end facing the light-receptive portion 41 of the light guide 9 has a concave surface adapted to the dome-shaped light-receptive portion 41, thereby four corners of the exit end projecting downward largely. This may cause an interference between the edge of the light guide 9 and the light-receptive portion 41 when the front panel 2 is attached to the main body of the receiver. In order to permit a smooth attachment of the front panel 2, a large space is needed between the two, thus the light sensitivity is lowered.